Dear Jim:
Many thanks for your response.
Yes I have highmemfix=1 in the graphics section and I don´t know if this disappear reverting to Dx9.
Any way, this is not the first time that this happens, in my previous computer with FS9 I had the same problem, but I don´t remember how I fixed, it was something like a kind of incompatibility with some application or something like that.
It´s really annoying, so if you have another idea it will be welcome.